Update config.sh

HA deployment on ubuntu with 3 nodes: 1 controller, 1 compute and 1 zabbix fails with "Deployment has failed. Timeout of deployment is exceeded." because of swapping. So, propose to update comment about minimum ubuntu RAM.

VERSION:
  feature_groups:
    - mirantis
    - experimental
  production: "docker"
  release: "5.1"
  api: "1.0"
  build_number: "11"
  build_id: "2014-09-17_21-40-34"
  astute_sha: "f5fbd89d1e0e1f22ef9ab2af26da5ffbfbf24b13"
  fuellib_sha: "d9b16846e54f76c8ebe7764d2b5b8231d6b25079"
  ostf_sha: "64cb59c681658a7a55cc2c09d079072a41beb346"
  nailgun_sha: "eb8f2b358ea4bb7eb0b2a0075e7ad3d3a905db0d"
  fuelmain_sha: "8ef433e939425eabd1034c0b70e90bdf888b69fd"